1. Field of the Invention
The present invention relates to a MEMS element and an electrical device using the same.
2. Description of the Related Art
Microelectromechanical systems (MEMS) are expected to be applied to many fields such as high-frequency/wireless, optics, acceleration sensors, biology and power. As for a MEMS element used as a resonator and the like, for example, MEMS resonators have been being developed. A MEMS resonator has advantages that it can be manufactured by a method that is compatible with semiconductor manufacturing method, which allows downsizing, integration and cost reduction comparing to conventional quartz resonators. Development of MEMS resonators is therefore expected as a technique that is supposed to greatly contribute to downsizing of resonators.
To put MEMS elements into practical use, sealing techniques are one of the important factors to be developed. Sealing techniques contribute to improvement of reliability of MEMS elements, and are important for maintaining the sealed internal atmosphere and protecting MEMS elements from external pollutants. With regard to MEMS resonators, for example, gas viscosity causes attenuation of the vibration energy (squeeze-film dumping), and the quality factor (Q factor), which represents sharpness of resonance, is decreased. In order to achieve a high Q factor, it is therefore required to vacuum-seal MEMS resonators, i.e. to keep the surroundings of MEMS resonators vacuum.
As mentioned above, MEMS elements often have a unique structure with a cavity, and specific sealing techniques have been being developed for MEMS elements. Such sealing techniques are broadly classified into bonding sealing by covering with a bonded cap substrate and thin-film sealing by covering with a thin film by thin film processing. The thin-film sealing can be performed by thin film processing that is continuous from the process of manufacturing MEMS elements, and is expected to reduce the cost of sealing techniques.
JP-A-2007-222956 discloses a sealing technique of forming a cavity by contacting with etching fluid at an opening of acid-resistant film such as silicon nitride film and then sealing the opening with resin or a board member.
JP-A-2008-137139 discloses a technique of forming a cavity by introducing etching fluid from a through hole of cavity forming film and then sealing it by forming sealing film of SiO2, SiN or the like onto the whole cavity forming film.